Most power semiconductor packages use copper or alloyed copper heat sinks such as CuMoCu or CuW as the flange upon which power semiconductor die are attached. A lid is typically attached to the flange to enclose and protect the die. During the die attach, lid attach and other package assembly processes, the metallic flange typically becomes bowed. The bowing occurs as a result of CTE (coefficient of thermal expansion) mismatches between the semiconductor die and the metal flange, for example. Attaching a bowed flange to a circuit board results in poor thermal performance because the flange and circuit board are not in good surface contact with one another. Instead, there is a gap between the flange and the circuit board. Having a gap between the flange and the circuit board significantly decreases thermal performance of the overall assembly, which is particularly problematic for high power applications. Materials such as thermal grease and indium solder foils have been used to fill the gap between a bowed flange and a circuit board to which the flange is fastened. However, thermal performance still suffers appreciably even with the use of gap filler materials since the least restrictive thermal pathway is direct contact between the flange and the circuit board.